diff --git a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/AbstractGeneratorMojo.java b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/AbstractGeneratorMojo.java
index 56c5c04..2f77aa0 100644
--- a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/AbstractGeneratorMojo.java
+++ b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/AbstractGeneratorMojo.java
@@ -34,6 +34,8 @@ import java.io.IOException;
 import java.util.Set;
 
 /**
+ * Abstract class for this Plugin.
+ *
  * @author <a href="mailto:jason@maven.org">Jason van Zyl</a>
  * @version $Id$
  */
@@ -89,8 +91,14 @@ public abstract class AbstractGeneratorMojo
      */
     protected Set/* <String> */extractors;
 
+    /**
+     * @return the output directory where files will be generated.
+     */
     protected abstract File getOutputDirectory();
 
+    /**
+     * @return the wanted <code>Generator</code> implementation.
+     */
     protected abstract Generator createGenerator();
 
     /** {@inheritDoc} */
diff --git a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/PluginReport.java b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/PluginReport.java
index c92037b..b02d0de 100644
--- a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/PluginReport.java
+++ b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/PluginReport.java
@@ -220,6 +220,11 @@ public class PluginReport
         return "plugin-info";
     }
 
+    /**
+     * @param pluginDescriptor not null
+     * @param locale not null
+     * @throws MavenReportException if any
+     */
     private void generatePluginDocumentation( PluginDescriptor pluginDescriptor, Locale locale )
         throws MavenReportException
     {
@@ -238,6 +243,10 @@ public class PluginReport
 
     }
 
+    /**
+     * @param locale not null
+     * @return the bundle for this report
+     */
     protected static ResourceBundle getBundle( Locale locale )
     {
         return ResourceBundle.getBundle( "plugin-report", locale, PluginReport.class.getClassLoader() );
@@ -258,6 +267,13 @@ public class PluginReport
 
         private final Locale locale;
 
+        /**
+         * @param project not null
+         * @param requirements not null
+         * @param sink not null
+         * @param pluginDescriptor not null
+         * @param locale not null
+         */
         public PluginOverviewRenderer( MavenProject project, Requirements requirements, Sink sink,
                                        PluginDescriptor pluginDescriptor, Locale locale )
         {
@@ -431,7 +447,7 @@ public class PluginReport
 
         /**
          * Render the section about the usage of the plugin.
-         * 
+         *
          * @param hasMavenReport If the plugin has a report or not
          */
         private void renderUsageSection( boolean hasMavenReport )
@@ -512,8 +528,8 @@ public class PluginReport
          * Try to lookup on the Maven prerequisites property.
          * If not specified, uses the value defined by the user.
          *
-         * @param project
-         * @param requirements
+         * @param project not null
+         * @param requirements not null
          * @return the Maven version
          */
         private static String discoverMavenRequirement( MavenProject project, Requirements requirements )
@@ -537,8 +553,8 @@ public class PluginReport
          * If not specified, uses the value defined by the user.
          * If not specified, uses the value of the system property <code>java.specification.version</code>.
          *
-         * @param project
-         * @param requirements
+         * @param project not null
+         * @param requirements not null
          * @return the JDK version
          */
         private static String discoverJdkRequirement( MavenProject project, Requirements requirements )
@@ -565,7 +581,7 @@ public class PluginReport
         }
 
         /**
-         * @param pluginsAsMap
+         * @param pluginsAsMap could be null
          * @return the value of the <code>target</code> in the configuration of <code>maven-compiler-plugin</code>.
          */
         private static String discoverJdkRequirementFromPlugins( Map pluginsAsMap )
diff --git a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/UpdatePluginRegistryMojo.java b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/UpdatePluginRegistryMojo.java
index d8f3bd2..a04e667 100644
--- a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/UpdatePluginRegistryMojo.java
+++ b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/UpdatePluginRegistryMojo.java
@@ -42,10 +42,10 @@ import java.util.Date;
 /**
  * Update the user plugin registry (if it's in use) to reflect the version we're installing.
  *
+ * @version $Id$
  * @since 2.0
  * @goal updateRegistry
  * @phase install
- * @version $Id$
  */
 public class UpdatePluginRegistryMojo
     extends AbstractMojo
@@ -104,13 +104,19 @@ public class UpdatePluginRegistryMojo
         }
     }
 
-    private void updatePluginVersionInRegistry( String groupId, String artifactId, String version )
+    /**
+     * @param aGroupId not null
+     * @param anArtifactId not null
+     * @param aVersion not null
+     * @throws MojoExecutionException if any
+     */
+    private void updatePluginVersionInRegistry( String aGroupId, String anArtifactId, String aVersion )
         throws MojoExecutionException
     {
         PluginRegistry pluginRegistry;
         try
         {
-            pluginRegistry = getPluginRegistry( groupId, artifactId );
+            pluginRegistry = getPluginRegistry( aGroupId, anArtifactId );
         }
         catch ( IOException e )
         {
@@ -121,7 +127,7 @@ public class UpdatePluginRegistryMojo
             throw new MojoExecutionException( "Failed to parse plugin registry.", e );
         }
 
-        String pluginKey = ArtifactUtils.versionlessKey( groupId, artifactId );
+        String pluginKey = ArtifactUtils.versionlessKey( aGroupId, anArtifactId );
         Plugin plugin = (Plugin) pluginRegistry.getPluginsByKey().get( pluginKey );
 
         // if we can find the plugin, but we've gotten here, the useVersion must be missing; fill it in.
@@ -130,12 +136,12 @@ public class UpdatePluginRegistryMojo
             if ( TrackableBase.GLOBAL_LEVEL.equals( plugin.getSourceLevel() ) )
             {
                 // do nothing. We don't rewrite the globals, under any circumstances.
-                getLog().warn( "Cannot update registered version for plugin {" + groupId + ":" + artifactId
+                getLog().warn( "Cannot update registered version for plugin {" + aGroupId + ":" + anArtifactId
                     + "}; it is specified in the global registry." );
             }
             else
             {
-                plugin.setUseVersion( version );
+                plugin.setUseVersion( aVersion );
 
                 SimpleDateFormat format =
                     new SimpleDateFormat( org.apache.maven.plugin.registry.Plugin.LAST_CHECKED_DATE_FORMAT );
@@ -147,19 +153,24 @@ public class UpdatePluginRegistryMojo
         {
             plugin = new org.apache.maven.plugin.registry.Plugin();
 
-            plugin.setGroupId( groupId );
-            plugin.setArtifactId( artifactId );
-            plugin.setUseVersion( version );
+            plugin.setGroupId( aGroupId );
+            plugin.setArtifactId( anArtifactId );
+            plugin.setUseVersion( aVersion );
 
             pluginRegistry.addPlugin( plugin );
 
             pluginRegistry.flushPluginsByKey();
         }
 
-        writeUserRegistry( groupId, artifactId, pluginRegistry );
+        writeUserRegistry( aGroupId, anArtifactId, pluginRegistry );
     }
 
-    private void writeUserRegistry( String groupId, String artifactId, PluginRegistry pluginRegistry )
+    /**
+     * @param aGroupId not null
+     * @param anArtifactId not null
+     * @param pluginRegistry not null
+     */
+    private void writeUserRegistry( String aGroupId, String anArtifactId, PluginRegistry pluginRegistry )
     {
         File pluginRegistryFile = pluginRegistry.getRuntimeInfo().getFile();
 
@@ -182,7 +193,7 @@ public class UpdatePluginRegistryMojo
             catch ( IOException e )
             {
                 getLog().warn( "Cannot rewrite user-level plugin-registry.xml with new plugin version of plugin: \'"
-                    + groupId + ":" + artifactId + "\'.", e );
+                    + aGroupId + ":" + anArtifactId + "\'.", e );
             }
             finally
             {
@@ -191,7 +202,14 @@ public class UpdatePluginRegistryMojo
         }
     }
 
-    private PluginRegistry getPluginRegistry( String groupId, String artifactId )
+    /**
+     * @param aGroupId not null
+     * @param anArtifactId not null
+     * @return the plugin registry instance
+     * @throws IOException if any
+     * @throws XmlPullParserException if any
+     */
+    private PluginRegistry getPluginRegistry( String aGroupId, String anArtifactId )
         throws IOException, XmlPullParserException
     {
         PluginRegistry pluginRegistry = null;
@@ -205,5 +223,4 @@ public class UpdatePluginRegistryMojo
 
         return pluginRegistry;
     }
-
 }
diff --git a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/metadata/AddPluginArtifactMetadataMojo.java b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/metadata/AddPluginArtifactMetadataMojo.java
index 04439ad..acdde91 100644
--- a/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/metadata/AddPluginArtifactMetadataMojo.java
+++ b/maven-plugin-plugin/src/main/java/org/apache/maven/plugin/plugin/metadata/AddPluginArtifactMetadataMojo.java
@@ -33,6 +33,7 @@ import org.apache.maven.project.MavenProject;
  * and deployment. The first use-case for this is to add the LATEST metadata (which is plugin-specific)
  * for shipping alongside the plugin's artifact.
  *
+ * @version $Id$
  * @since 2.0
  * @phase package
  * @goal addPluginArtifactMetadata
@@ -40,7 +41,6 @@ import org.apache.maven.project.MavenProject;
 public class AddPluginArtifactMetadataMojo
     extends AbstractMojo
 {
-
     /**
      * The project artifact, which should have the LATEST metadata added to it.
      *
@@ -57,6 +57,7 @@ public class AddPluginArtifactMetadataMojo
      */
     private String goalPrefix;
 
+    /** {@inheritDoc} */
     public void execute()
         throws MojoExecutionException
     {
@@ -74,6 +75,9 @@ public class AddPluginArtifactMetadataMojo
         projectArtifact.addMetadata( groupMetadata );
     }
 
+    /**
+     * @return the goal prefix parameter or the goal prefix from the Plugin artifactId.
+     */
     private String getGoalPrefix()
     {
         if ( goalPrefix == null )